1. Field of the Invention
The present invention relates to a method of producing bisphosphine oxide from phosphine oxide having carboxylic acid group through a Kolbe electrolysis coupling reaction.
2. Description of the Prior Art
In recent years, the ratio of the optically active medicine of all the medicine in the market is increasing year after year. In the last five years, the optically active medicine amounts to 39% of the share. Moreover, the need for optically active substances is not limited to the field of medicine, but extends to fields such as agricultural chemicals, perfume, and even high-performance materials such as ferroelectric liquid crystal and packings for high performance liquid chromatography. One of the methods for synthesizing these optically active compounds is the catalytic asymmetric synthesis. The catalytic asymmetric synthesis method is considered as an excellent method for economically obtaining large amounts of pure optically active compound from prochiral compound. Numerous development of asymmetric catalyst has been conducted in the last 20 years. Especially, rhodium and ruthenium complex having optically active phosphine as a ligand has been studied.
Of the compounds having optically active phosphine as a ligand as mentioned above, a bisphosphine compound having a wide accommodation range of reaction temperature, and especially having high asymmetry recognition ability under high temperature and high pressure is preferred. This optically active bisphosphine compound may be obtained by reducing bisphosphine oxide while maintaining its asymmetry using hexachlorodisilane. (K. Naumann, G. Zon, and K. Mislow, J. Am. Chem. Soc., 91, 7012 (1969)).
Of the methods of producing optically active bisphosphine oxide, the most common method known is to perform an oxidation coupling of the optically active phosphine oxide having methyl group with an organolithium compound such as LDA (lithium diisopropylamide) and copper compound such as copper chloride. (B. D. Vineyard, w. S. Knowles, M. J. Sabacky, G. L. Backman and O. J. Weinkauff, J. Am. Chem. Soc., 99, 5946 (1977)). ##STR3##
However, the organolithium compound used in these methods is very active to air, water and the like, so not only it is difficult to industrialize, but it is also difficult to perform economically since it concerns the separation of by-products of metal impurity such as copper salt and the like.